1. Field of the Invention
The present invention relates to Q-switching apparatus for use in controlling laser emission. More particularly, it relates to a controller for controlling a Q-switch of a laser device operating in a long-pulse mode.
2. Description of the Related Art
A typical switched cavity laser system includes a gain medium and a Q-switch disposed in a resonant cavity, and a pump, such as a flash lamp, for providing energy to the gain medium. The Q-switch toggles the Q factor of the cavity between high and low values, to allow or prevent lasing action, respectively, according to a variety of operating modes. The fundamentals of laser Q-switching are taught in Koechner, Solid-State Laser Engineering, 2d ed., pp. 402-446, Springer-Verlag (1988), and are incorporated herein by reference.
The Q-switch is generally used in "short-pulse" mode, to generate output laser beam pulses of very short duration but high intensity. In this mode, the Q-switch is closed and the pump is turned on. The Q-switch is reopened after the pump has stored energy in the form of a population inversion Within the gain medium. When the Q-switch is opened, a short pulse of laser energy is generated. Short-pulse beams are useful in many high-energy applications of the laser device, such as drilling or machining of a workpiece.
However, lower intensity beams are required for alignment and adjustment of the resonant cavity, for pre-drilling focusing or aiming of the beam, and for other purposes. In such applications, the high-intensity pulses of the short-pulse mode might damage alignment or testing equipment, or might cause drilling to occur at unwanted points on the workpiece.
To produce lower intensity pulses, these switched cavity systems are operated in a "long-pulse" mode. In the long-pulse mode, the Q-switch is opened at the same time the pump is turned on, so that no energy is stored in the gain medium, and the pump energy is coupled directly into the output beam. The Q-switch is closed at a fixed time later, normally after shutting off the pump. Long-pulse mode operation generates relatively long duration pulses of laser energy of relatively low intensity.
The energy of a long-pulse beam has been controlled in the prior art by controlling the intensity of the pump energy. However, pump control devices are costly and unwieldy, and provide minimal precision in controlling the long-pulse mode. A need exists for an inexpensive and convenient apparatus and method of providing precise control over the long-pulse operation of a laser device.